Spectral decomposition’ application images early-Cretaceous tectonically-controlled shallow-marine unconventional shale gas-bearing resources, SW-Asian Indus rift basin: Inverted velocity and density structural simulations

Abstract

Incised marine valleys (IV) are hot topics in unconventional shale gas exploration. These depositional systems are developed during the rapid fall and subsequent slow rise in the sea level. The reservoir shale lenses are trapped in the naturally fractured shale facies of IV. Therefore, the natural fractures and fault systems inside this IV have an enormous impact on the perpendicular and horizontal movement of hydrocarbon-posture fluids. Every combination trap of a petroleum system has an exact fine-tuning frequency, which can remain useable for resolving the reservoir and seal. This study develops a cost-economic petroleum system using seismic attributes, broadband spectral decomposition-based inverted density structural simulation and inverted velocity structural simulation for imaging natural fractures and fault systems in the SW-Asian onshore Indus rift basin. A band-pass frequency filter of 6–22-48-62 Hz was applied on the IV with two lower-peak and higher-peak tuning frequencies of 22-Hz and 48-Hz. The 22-Hz tuning frequency resolves this IV architecture at its greatest plausible location of gas-posture reserves. The traditional mapping shows poor competence to image a fractured system. The 22-Hz frequency has resolved the dense fracture system in the westernmost region. 48-Hz frequency has resolved the top seal of fracture-less zones to provide high-density zones to stop vertical migrations of gas-bearing fluids inside the reservoir shale lenses of IV. The inverted velocity structural simulations have poorly imaged the E-W transforms fault. The 22-Hz frequency-based inverted density structural simulations have resolved the en-echelon geometry along a high-amplitude anomalous and E-W oriented transform fault from a point of inflexion of fractured reservoir shale lenses from source to reservoir beds of IV. The lateral extent of this en-echelon structure is ∼1.35 km with a vertical depth of ∼3281–3299 m. The inverted density structural simulation has resolved two transform faults, which were imaged at depths of 3282 and 3298 m. The zone between pseudo-densities of 2.1–2.4 g/c.c shows uniform sedimentations inside the IV. This implicates the deposition of laterally continuous and fractured fluvial-dominated reservoir shale reservoir lenses. The inverted density structural simulations have also resolved the least angle (<∼2^o) of the combination trap at pseudo-densities of 2.1–2.4 gm./c.c. No vertical amplitude anomaly could be imaged for predicting the intensity of fractures and upward migration from source to reservoir beds, which implicates the regionally established traps inside the IV. The fractured reservoir has accumulated the shale gas-bearing fluids inside the IV, which implicates the tectonic subsidence. The combination trap experiences inclinations increase to 35^o at a 2.6 gm./c.c pseudo-density. Hence, inverted density structural simulation shows strong implications for the horizontal migrations of shale gas resources inside the IV. Consequently, conducted exploration strategies may serve as an analogue for the SW-Asian Indus Onshore rift basin and similar structural basins.